BACKGROUND: Several animal experiments utilizing bone marrow stromal cell (BMSC) transplantation for the treatment of spinal cord injury have proposed a hypothesis that BMSC transplantation effects are associated with increased glial cell-derived neurotrophic factor (GDNF) expression.OBJECTIVE: To confirm the effects of BMSC transplantation on GDNF mRNA expression in rats with spinal cord injury by reverse transcription-polymerase chain reaction (RT-PCR).DESIGN, TIME AND SETTING: The present molecular, cell biology experiment was performed at the Key Laboratory of Children's Congenital Malformation, Ministry of Health of China & Department of Developmental Biology, Basic Medical College, China Medical University between March 2006 and May 2007.MATERIALS: Sixty healthy Wistar rats aged 2--4-months and of either gender were included in this study. Spinal cord injury was induced in all rats by hemisection ofT9 on the left side. RT-PCR kits were purchased from TaKaRa Company, China. Type 9600 RCR amplifier was provided by PerkinElmer Company, USA. METHODS: Three rats were selected for BMSC culture and subsequent transplantation (after three passages). Of the remaining 57 rats, nine were selected for sham-operation (sham-operated group), where only the T9 spinal cord was exposed without hemisection. A total of 48 rats were randomly and evenly divided into BMSC transplantation and model groups. In the BMSC transplantation group, following spinal cord injury induction, each rat was administered a BMSC suspension through two injection sites selected on the gray and white matter boundary caudally and cephalically, seperately and near to injury site in the spinal cord. The model group received an equal volume of PBS through the identical injection sites.MAIN OUTCOME MEASURES: At 24 and 72 hours, as well as at 7 days, following spinal cord injury, the spinal cord at the T9 segment was removed. Eight rats were allocated to each time point in the BMSC transplantation and model groups, with three rats allocated to the sham-operated group. GDNF mRNA expression was semiquantitatively analyzed by RT-PCR.RESULTS: The sham-operated group exhibited extremely low GDNF mRNA expression. GDNF mRNA expression significantly increased at 24 hours after spinal cord injury, reached a peak level at 72 hours, and slowly decreased thereafter. However, it remained higher than normal levels at 7 days (P < 0.05). At all time points following spinal cord injury, GDNF mRNA expression was significantly greater in the BMSC transplantation group than in the model group (P < 0.05).CONCLUSION: Transplantation of BMSCs into the injured spinal cord up-regulated GDNF mRNA expression, thereby promoting repair of the injured spinal cord.